Campylostoma matutiforme Bell, 1858

Van Bakel, Barry W. M., Guinot, Danièle, Artal, Pedro, Fraaije, René H. B. & Jagt, John W. M., 2012, A revision of the Palaeocorystoidea and the phylogeny of raninoidian crabs (Crustacea, Decapoda, Brachyura, Podotremata) 3215, Zootaxa 3215 (1), pp. 1-216 : 57-58

Campylostoma matutiforme Bell, 1858

( Fig. 16A–F )

Material examined. Partial carapace with mxp3, London Clay , Ypresian , lower Eocene , Herne Bay , Kent, England ( NHM In. 32654/32655); syntype, carapace with sternite 4, P1 coxae and mxp3, London Clay, Ypresian, lower Eocene, Isle of Sheppey, England ( NHM In. 7314); partial carapace with sternite 4, abdomen and bases of pereiopods, same provenance ( NHM In. 35231); 2 carapaces, same provenance ( NHM In. 39424, In. 59083) .

Emended description. Pleural suture distinct, running just below anterolateral, posterolateral margins. Pterygostome large, anteriorly tumid, with blunt granular crest, extended anteriorly into prominent subantennary lobe; buccal cavity narrow, margins weakly concave, rimmed. Mxp3: coxae large, flabelliform, inserted in front of P1; exopod relatively short, wedge shaped with narrow distal end; endopod elongated, slender, basis-ischium, merus equally long, merus strongly grooved. Sternites 3‒6 preserved; sternite 3 small, incompletely preserved, separated from sternite 4 by oblique lateral grooves; sternite 4 trapezoidal, lateral sides weakly raised, lateral margins slightly concave, nearly vertical groove at level of P1 gynglyme separating large raised episternite 4; episternite 5 raised, oblique, at least one prominence present for abdominal holding; sutures 4/5, 5/6 similarly shaped, only lateral, crescent shaped, medial part vertical, demarcating flat, undivided medial floor of sternum. Abdomen curvature in prolongation with carapace, all somites free, somite 1 short, wide, somite 3 narrowest, somites 3‒5 with raised medial ridge, which is strong, acute in somite 4, somite 6 longer, telson unknown. P1‒P 3 in the same level, P4 weakly tilted, slightly reduced, P5 subdorsal, strongly reduced.

Remarks. Study of the material examined necessitates an amendment of the description; the carapace was described by Bell (1858: 23) and Carter (1898: 30). Campylostoma matutiforme (see Bell 1858: 23, pl. 3, figs. 8– 10) was deemed a podotreme crab, possibly a cenomanocarcinid, by Guinot et al. (2008: 21). The re-examination of several specimens in the NHM collections ( Fig. 16A–F ) confirm this placement. The much elongated mxp3 with large, flabelliform coxae, sculpture of the pterygostome with pronounced, pointed subantennary lobes, crownshaped sternite 3, subtrapezoidal sternite 4, match the cenomanocarcinid configuration. The carapace does not show the strong branchial crests that are typical of Cenomanocarcinus spp. , and the orbits are much wider. The presence of an abdominal holding system on episternite 5 is confirmed in one specimen, where a single, sharp tubercle is visible; because of poor preservation, it is unclear if a more posteriorly situated peg was present.

Figures

FIGURE 16. Campylostoma matutiforme Bell, 1858 (Cenomanocarcinidae); A, D–F, NHM In. 35231 (male), lower Eocene (Ypresian), Sheppey (Kent, southern England); ventral, posterior, left lateral, and abdominal views; B, C, NHM In. 32654/ 32655 (indeterminate sex), lower Eocene (Ypresian), Herne Bay (Kent, southern England); frontal and ventral views latter showing pterygostomes and mxp3. a1, a2, a3, a4, a5, a6, abdominal somites 1, 2, 3, 4, 5, 6; cx1, cx2, cx3, cx4, cx5, P1, P2, P3, P4, P5 coxas; lb, linea brachyura; P1, P2, P3, P4, pereiopods 1, 2, 3, 4; pt, pterygostome; sl, subantennary lobe of pterygostome. Scale bars: A-E: 5mm; F: 2mm.